ESD Clamp for NxVDD Rail Using NMOS Stack and Detector
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Solution Overview
Problem
Conventional ESD protection circuits in CMOS circuits face challenges in maintaining reliability due to increased complexity and reduced size, which can lead to overstressing of thinner gate-oxides and susceptibility to electro-static discharge events, especially when the gate-oxide is scaled down.
Innovation Solution
An electro-static discharge clamp is designed using an NMOS stack with a detector that controls the gate nodes, featuring three switches to manage the flow of ESD current during normal and ESD events, employing configurations such as RC inverters, diode strings, and latch circuits to effectively route the current to ground, thereby protecting the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If gate-oxide thickness is scaled down to increase circuit operating speed, then circuit operating speed is improved, but gate-oxide becomes overstressed and more susceptible to ESD damage
Solution Approach 1:
The ESD protection function is segmented from the main power supply path by using a separate detection mechanism (RC inverter or latch circuit) that independently monitors voltage conditions and activates the clamp transistor only when ESD events are detected, rather than having the clamp transistor continuously connected to the power rail
Solution Approach 2:
An intermediary detection circuit (RC inverter or latch circuit) is introduced between the power supply voltage and the clamp transistor gate, which translates voltage conditions into controlled activation of the ESD protection path, preventing direct overstress on the gate-oxide while maintaining protection capability
2Reliability
If conventional ESD clamp transistor is used with thin gate-oxide, then ESD protection is provided, but the clamp transistor itself becomes vulnerable to damage
Solution Approach 1:
The detection circuit performs preliminary detection of ESD conditions through the RC inverter or latch circuit before activating the clamp transistor, ensuring the protection path is activated only when actually needed and not subjected to unnecessary voltage stress during normal operation
Solution Approach 2:
The clamp transistor's state is dynamically controlled based on detected conditions - remaining in high-impedance state during normal operation and switching to active conduction state only during ESD events, adapting its behavior to the actual threat level
3Use of energy by moving object
If power supply voltage is reduced for low-power applications, then power consumption is reduced, but ESD protection becomes more critical
Solution Approach 1:
The ESD detection circuit is self-powered from the same power supply it protects, using the voltage present on the power rail itself to drive the RC inverter or latch circuit, eliminating the need for separate power sources while maintaining continuous monitoring capability
Solution Approach 2:
The detection circuit provides feedback about voltage conditions to the clamp transistor through the controlled switching mechanism, creating a closed-loop system that automatically responds to ESD threats without external control while consuming minimal power
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the reliability of CMOS circuits by effectively managing ESD events without overstressing the gate-oxide, ensuring the circuit can withstand high-voltage discharges and maintaining operational integrity.
Implementation Method 1
An electro-static discharge detector is configured to control the NMOS stack
Implementation Method 2
the first switch may be a capacitor or a diode string
Implementation Method 3
the first switch may be a capacitor or a diode string
Implementation Method 4
the clamp transistor will turn 'on,' thereby shunting the induced ESD potential to ground
Data Source
AI summary
A circuit with an electro-static discharge clamp coupled to a first power source and second power source. The electro-static discharge clamp includes an NMOS stack and an electro-static discharge detector. The NMOS stack has a first NMOS transistor with gate node ng1 and a second NMOS transistor with gate node ng2. The electro-static discharge detector is configured to control the NMOS stack, and may include three switches. A first switch is configured to switch the gate node ng1 to the second power source. A second switch is configured to switch the gate node ng1 to the gate node ng2. A third switch is configured to switch the gate node ng1 to the ground.